There is a lithium secondary battery in which a cell is sealed with an outer film. In such a lithium secondary battery, a positive electrode current collector, a positive electrode active material layer, an electrolyte layer, a negative electrode active material layer, and a negative electrode current collector are stacked to form a cell, and the cell is sealed with an outer film. In the lithium secondary battery, a positive electrode terminal and a negative electrode terminal that are exposed to the outside are provided.
For example, in a lithium secondary battery (polymer lithium ion secondary battery) according to Japanese Patent Application Laid-Open No. 11-312514 (1999), a positive electrode active material layer and a negative electrode active material layer are formed on a surface of a positive electrode current collector and a surface of a negative electrode current collector, respectively, to prepare a positive electrode side composite body in which the positive electrode current collector is integrated with the positive electrode active material layer and a negative electrode side composite body in which the negative electrode current collector is integrated with the negative electrode active material layer (paragraph 0007). A positive electrode terminal and a negative electrode terminal (leads) are connected to the positive electrode current collector and the negative electrode current collector, respectively (paragraph 0008). An electrolyte layer is arranged between the positive electrode side composite body and the negative electrode side composite body (paragraph 0008). A stack of the positive electrode current collector, the positive electrode active material layer, the electrolyte layer, the negative electrode active material layer, and the negative electrode current collector is sealed with an outer film (laminated film) (paragraph 0008).
In a lithium secondary battery according to Japanese Patent Application Laid-Open No. 11-97070 (1999), a positive electrode active material layer and a negative electrode active material layer are formed on a surface of a positive electrode current collector and a surface of a negative electrode current collector, respectively, to prepare a positive electrode side composite body (positive electrode) in which the positive electrode current collector is integrated with the positive electrode active material layer and a negative electrode side composite body (negative electrode) in which the negative electrode current collector is integrated with the negative electrode active material layer (paragraph 0044). A positive electrode terminal (positive electrode lead) and a negative electrode terminal (negative electrode lead) are connected to the positive electrode current collector and the negative electrode current collector, respectively (paragraph 0048). An electrolyte layer is arranged between the positive electrode side composite body and the negative electrode side composite body (paragraph 0048). A stack of the positive electrode current collector, the positive electrode active material layer, the electrolyte layer, the negative electrode active material layer, and the negative electrode current collector is sealed with a two-folded outer film (composite film) (paragraph 0049).